Twin-roll strip caster and casting method using same

ABSTRACT

A twin-roll strip caster includes: a pair of casting rolls rotating in opposite directions to each other, and having an edge dam adhering to both end surfaces of the casting rolls in a length direction of the casting rolls; a submerged nozzle discharging molten steel between the pair of casting rolls; a meniscus shield disposed above the molten steel supplied through the submerged nozzle to prevent the molten steel from contacting air; and a focused gas supply nozzle disposed between the submerged nozzle and the meniscus shield to supply inert gas therebetween so as to displace air between the submerged nozzle and the meniscus shield before the molten steel is supplied.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean Patent Application No. 10-2015-0157693, filed on Nov. 10, 2015 with the Korean Intellectual Property Office, the entirety of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to an improved twin-roll strip caster, which may reduce scum in a process of manufacturing a strip coil, and a casting method using the same.

In general, a twin-roll strip casting process is provided as a method of supplying molten steel to two rotating casting rolls, and continuously manufacturing a steel, for example, a strip from the molten steel.

In a twin-roll strip caster, molten steel is supplied to a space between a pair of casting rolls and edge dams disposed on end surfaces of the casting rolls, and the molten steel is cooled on the surfaces of the casting rolls, while rotating, to thus manufacture steel having a reduced thickness, for example, a strip.

Furthermore, since molten steel supplied through a nozzle may be oxidized as the surface of a pool of molten steel comes into contact with air, an oxidation prevention cover for a pool of molten steel, such as a meniscus shield, is commonly installed above casting rolls, and inert gas is dispensed to a space between a lower portion of the cover and a pool of molten steel. Accordingly, the molten steel of the pool of molten steel contacts the inert gas, and is thus prevented from contacting air. Thus, oxidation of the molten steel may be maximally controlled.

However, a twin-roll strip caster of the related art may have a space surrounding the surface of a pool of molten steel, and the space may not be tightly sealed, which may cause molten steel to be oxidized by air present in an early stage of a casting process or by bubbles generated in the casting process. Thus, an oxidized byproduct, known as scum, may float on the surface of the pool of molten steel.

Such scum may cause defects when mixed with a casting material, and thus, the flow of molten steel is controlled so that scum is not mixed with the casting material, or a dam is installed on the surface of the molten steel pool so that scum cannot approach casting rolls, thereby preventing scum from being mixed with the casting material.

In an example, in order to prevent the oxidation of molten steel surrounded by casting rolls and an edge dam by molten steel pool surface protection technology of the related art, a sealing apparatus capable of blocking an external oxidative atmosphere while adjusting the depth, from the surface of a pool of molten steel, of a submerged nozzle, has been proposed in Japanese Patent Publication No. 1994-297111.

Japanese Patent Publication No. 1994-297111 allows the depth of a submerged nozzle to be adjusted by controlling a spring, installed on the lateral surface of a tundish, when changing the level of the surface of a pool of molten steel during a casting process, and enables the atmosphere of an upper portion of the surface of the molten steel pool to remain constant according to changes in the level of the surface.

Furthermore, Japanese Patent Publication No. 1995-204795 refers to a technology of preventing oxides, generated on the surface of a pool of molten steel, from being mixed with solidified shells by installing a long dam having a portion submerged in the molten steel pool, and allows the surfaces of casting rolls and the long dam to be spaced from each other by a small gap, and an upper portion of the surface of the molten steel pool to remain under an inert gas atmosphere while maintaining the level of the surface of the molten steel pool at that of the small gap, thus minimizing the generation of oxides and preventing oxides from being mixed with growing solidified shells.

Moreover, Korean Patent Publication No. 10-2003-0017073 has proposed a twin-roll strip caster having a gas knife cover member for maintaining an upper portion of the surface of a pool of molten steel under an inert atmosphere.

Such molten steel pool surface protection technology of the related art has been focused on a sealing function for preventing ingress of an external oxidative atmosphere. In addition, oxides generated on the surface of the molten steel pool are blocked by an apparatus known as a long dam or a weir, such that the oxides are not mixed with a casting material, and when an excessive amount of oxides cover the entirety of the surface of the molten steel pool, these oxides may not be entirely blocked, and a portion thereof may be mixed with the casting material.

In the related art, there has been progress in technology of preventing scum from being mixed with a casting material when scum is formed, but technology of preventing reoxidation of the surface of a pool of molten steel that may occur in an early stage of a casting process has not yet been developed.

This may cause the twin-roll strip caster of the related art to have difficulties in creating a completely inert atmosphere in a space between a submerged nozzle and a meniscus shield before molten steel is supplied, as an edge dam and the submerged nozzle of the twin-roll strip caster are preheated while being dismantled before the casting process and the edge dam and the submerged nozzle are assembled for use immediately after the casting process, in order to minimize temperature variations.

SUMMARY

An aspect of the present disclosure provides an improved twin-roll strip caster, which may rapidly create an inert atmosphere in order to prevent oxidation of molten steel caused by air remaining between casting rolls and a meniscus shield in an early stage of a casting process, and a casting method using the same.

According to an aspect of the present disclosure, a twin-roll strip caster includes: a pair of casting rolls rotating in opposite directions to each other, and having an edge dam adhering to both end surfaces of the casting rolls in a length direction of the casting rolls; a submerged nozzle discharging molten steel between the pair of casting rolls; a meniscus shield disposed above the molten steel supplied through the submerged nozzle to prevent the molten steel from contacting air; and a focused gas supply nozzle disposed between the submerged nozzle and the meniscus shield to supply inert gas therebetween so as to displace air between the submerged nozzle and the meniscus shield before the molten steel is supplied.

The focused gas supply nozzle may be disposed in the meniscus shield to dispense the inert gas to surfaces of the pair of casting rolls between the submerged nozzle and the edge dam.

The focused gas supply nozzle may dispense the inert gas from above one casting roll to a surface of the other casting roll.

The focused gas supply nozzle may include a first focused gas supply nozzle dispensing the inert gas from above the one casting roll, positioned at one end of the submerged nozzle in a width direction, to the surface of the other casting roll, and a second focused gas supply nozzle dispensing the inert gas from above the other casting roll, positioned at the other end of the submerged nozzle in the width direction, to the surface of the one casting roll.

According to an aspect of the present disclosure, a casting method for a twin-roll strip caster includes: an assembling operation of combining a pair of casting rolls, a preheated edge dam, a preheated submerged nozzle, and a meniscus shield with one another; an inert gas supplying operation of displacing air remaining between the pair of casting rolls and the meniscus shield by supplying inert gas therebetween at high pressure before molten steel is supplied through the preheated submerged nozzle after the assembling operation; and a casting operation of supplying the molten steel through the submerged nozzle after air is displaced by the inert gas supplying operation.

The inert gas supplying operation may include supplying the inert gas between the preheated edge dam and the preheated submerged nozzle.

The inert gas supplying operation may further include an air discharging operation of discharging air remaining between the pair of casting rolls and the meniscus shield while the inert gas is supplied.

The inert gas supplied in the inert gas supplying operation may be supplied at a flow rate of 500 liter/min to 2,500 liter/min.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the present disclosure will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of a twin-roll strip caster;

FIG. 2 is a partially enlarged view of a twin-roll strip caster according to an exemplary embodiment;

FIG. 3 is a plan view of a portion of a twin-roll strip caster according to an exemplary embodiment; and

FIG. 4 is a graph illustrating the relationship between a supplied amount of nitrogen and an oxygen removal time obtained from a twin-roll strip caster according to an exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described as follows with reference to the attached drawings.

The present disclosure may, however, be exemplified in many different forms and should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

Throughout the specification, it will be understood that when an element, such as a layer, region or wafer (substrate), is referred to as being “on,” “connected to,” or “coupled to” another element, it can be directly “on,” “connected to,” or “coupled to” the other element or other elements intervening therebetween may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element, there may be no other elements or layers intervening therebetween. Like numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be apparent that though the terms first, second, third, etc. may be used herein to describe various members, components, regions, layers and/or sections, these members, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one member, component, region, layer or section from another region, layer or section. Thus, a first member, component, region, layer or section discussed below could be termed a second member, component, region, layer or section without departing from the teachings of the exemplary embodiments.

Spatially relative terms, such as “above,” “upper,” “below,” and “lower” and the like, may be used herein for ease of description to describe one element's relationship relative to another element(s) as shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “above,” or “upper” relative to other elements would then be oriented “below,” or “lower” relative to the other elements or features. Thus, the term “above” can encompass both the above and below orientations depending on a particular direction of the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

The terminology used herein describes particular embodiments only, and the present disclosure is not limited thereby. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, members, elements, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, elements, and/or groups thereof.

Hereinafter, embodiments of the present disclosure will be described with reference to schematic views illustrating embodiments of the present disclosure. In the drawings, for example, due to manufacturing techniques and/or tolerances, modifications of the shape shown may be estimated. Thus, embodiments of the present disclosure should not be construed as being limited to the particular shapes of regions shown herein, for example, to include a change in shape results in manufacturing. The following embodiments may also be constituted by one or a combination thereof.

The contents of the present disclosure described below may have a variety of configurations and only a required configuration is proposed herein, but the present disclosure is not limited thereto.

FIG. 1 is a diagram of a twin-roll strip caster. FIG. 2 is a partially enlarged view of a twin-roll strip caster according to an exemplary embodiment. FIG. 3 is a plan view of a portion of a twin-roll strip caster according to an exemplary embodiment.

Referring to FIGS. 1 through 3, a twin-roll strip caster 100 according to an exemplary embodiment may continuously supply molten steel stored in a ladle 110 through a tundish 112 to manufacture a steel, for example, a strip.

For this purpose, the twin-roll strip caster 100 illustrated in FIG. 1 may include a pair of casting rolls 120 spaced apart from each other at a distance, and disposed opposite each other. Such casting rolls 120 may be rotated in opposite directions to each other to thus be respectively rotated in a direction in which the molten steel is supplied.

An edge dam 122 may also be disposed on end surfaces of the pair of casting rolls 120 to shield both ends of the casting rolls 120 in a length direction thereof.

The pair of casting rolls 120 and the edge dam 122 may also have a submerged nozzle 130 disposed in a space therebetween, and molten steel may be discharged through molten steel discharging portion formed in the submerged nozzle 130.

As such, the molten steel may be supplied to the space between the pair of casting rolls 120 and the edge dam 122 through the submerged nozzle 130 from the tundish 112 to form a pool of molten steel M, and the molten steel of the molten steel pool M may be cooled between the casting rolls 120 to be manufactured into a steel S.

Here, each of the casting rolls 120 may have a cooling unit disposed therein. Thus, the molten steel may lose heat while contacting the casting rolls 120, and resulting solidified shells may thus be formed from a surface of the molten steel. The solidified shells formed in this manner may be combined with those supplied by the other casting roll of the casting rolls 120 to manufacture the steel S, for example, a strip in complete form.

The twin-roll strip caster 100 may also include a meniscus shield 140 blocking air above the molten steel pool M of the molten steel supplied through the submerged nozzle 130, and blocking inert gas from leaking so as to prevent oxygen contained in air from contacting the molten steel.

The meniscus shield 140 may also include a sealing member 142 disposed on a portion of the meniscus shield 140 contacting each of the casting rolls 120, and on a portion of the meniscus shield 140 on which the submerged nozzle 130 passes. The meniscus shield 140 may also include a weir 144 disposed on one side thereof, and disposed adjacent to each of the casting rolls 120 in a width direction thereof, in order to block scum, formed on the surface of the molten steel pool M, from being mixed with a casting strip.

The meniscus shield 140 may include a full-width inert gas nozzle (not illustrated) supplying inert gas in the width direction of the casting rolls 120.

As a sealing state of the meniscus shield 140 is good, the meniscus shield 140 may remain under high internal pressure even when a small amount of inert gas is supplied.

The reason why the meniscus shield 140 needs to seal the moving casting rolls 120 and edge dam 122 is that forming a high level of sealing is impossible, and that the inert gas slightly may escape between the casting rolls 120 and the meniscus shield 140 and between the edge dam 122 and the meniscus shield 140 in an amount. Also, even in a case in which there is a gap between the casting rolls 120 and the meniscus shield 140 and between the edge dam 122 and the meniscus shield 140, so that the inert gas may slightly escape from the gap, when the supplied inert gas flow increases sufficiently, the meniscus shield 140 may generate positive pressure, regardless of the leakage of a small amount of inert gas, to prevent oxygen from flowing into the molten steel. Furthermore, the meniscus shield 140 may need to supply a larger amount of inert gas to generate positive pressure when the gap between the casting rolls 120 and the meniscus shield 140 and between the edge dam 122 and the meniscus shield 140 is very large.

The twin-roll strip caster 100 may be preheated while being disassembled before the early stage of a casting process, and may be assembled before the casting process in order to significantly reduce changes in temperature thereof.

For example, immediately before the casting process, the pair of casting rolls 120 and the preheated edge dam 122 disposed on end surfaces of the casting rolls 120 in the width direction thereof may be combined with each other in the twin-roll strip caster 100, and the preheated submerged nozzle 130 may be disposed between the casting rolls 120 to discharge the molten steel.

Immediately before the casting process, the twin-roll strip caster 100 may have limitations in that air containing oxygen may remain between the casting rolls 120 and the meniscus shield 140, and in that air may not be rapidly displaced only with an amount of inert gas supplied through the full-width gas supply nozzle disposed in the meniscus shield 140.

Thus, the twin-roll strip caster 100 illustrated in FIG. 2 may include a focused gas supply nozzle 150 supplying inert gas between the casting rolls 120 and the meniscus shield 140, in order to displace air between the casting rolls 120 and the meniscus shield 140 before the molten steel is supplied, immediately after the casting rolls 120, the edge dam 122, and the submerged nozzle 130 are combined with one another.

The focused gas supply nozzle 150 illustrated in FIG. 2 may be disposed in the meniscus shield 140. Here, the focused gas supply nozzle 150 may dispense the inert gas on the surfaces of the casting rolls 120 between the submerged nozzle 130 and the edge dam 122.

The focused gas supply nozzle 150 may, for example, dispense the inert gas within a range in which contact between the inert gas and the preheated submerged nozzle 130 and edge dam 122 is significantly reduced, in order to prevent the preheated submerged nozzle 130 and edge dam 122 from being changed in temperature.

In an example, a distance d1 between the focused gas supply nozzle 150 and the edge dam 122 and a distance d2 between the focused gas supply nozzle 150 and a lateral surface of the submerged nozzle 130 may be, for example, the same as each other.

The inert gas supplied through the focused gas supply nozzle 150 may be supplied to the space between the casting rolls 120 and the meniscus shield 140, and in this process, the supplied inert gas may displace air containing oxygen, and remaining between the casting rolls 120 and the meniscus shield 140. When the molten steel starts to be supplied through the submerged nozzle 130, the molten steel may be in contact with the inert gas after the displacement of air, and scum may thus be prevented from being generated.

Here, the inert gas may prevent scum from being generated when contacting the molten steel, and may be, for example, nitrogen (N2) gas or argon (Ar) gas.

As illustrated in FIG. 2, the focused gas supply nozzle 150 is illustrated as being disposed in the meniscus shield 140, but may be disposed to dispense the inert gas from above one of the casting rolls 120 to the other casting roll by the medium of a separate frame or the like.

For example, the focused gas supply nozzle 150 may be divided into a first focused gas supply nozzle and a second focused gas supply nozzle.

Here, the first focused gas supply nozzle may dispense the inert gas from above one of the casting rolls 120, disposed at one end of the submerged nozzle 130 in a width direction thereof, to a surface of the other casting roll, and the second focused gas supply nozzle may dispense the inert gas from above the other casting roll, disposed at the other end of the submerged nozzle 130 in the width direction thereof, to the surface of the one casting roll.

The first and second focused gas supply nozzles may be alternately disposed with each other to dispense the inert gas to the surfaces of the casting rolls 120 at an inclined angle.

The focused gas supply nozzle 150 illustrated in FIG. 2 may supply, for example, the inert gas at a flow rate of 500 liter/min to 2,500 liter/min in order to rapidly displace air.

When the inert gas is supplied at a flow rate of 500 liter/min or less, a sufficient amount of air may not be displaced before the molten steel is supplied in the early stage of the casting process. Thus, scum may be generated on the molten steel pool M in the early stage of the casting process.

Also, as the supply of the inert gas increases, the concentration of oxygen rapidly drops. For example, the inert gas supplied to the space between the casting rolls 120 and the meniscus shield 140 may not need to be supplied at a flow rate of 2,500 liter/min or greater, and it may be efficient that the inert gas is managed to be supplied at a flow rate of 2,500 liter/min or less with consideration of cost effectiveness or the like.

The twin-roll strip caster 100 illustrated in FIG. 2 may further include an air discharging unit 160 discharging air, in order to increase a rate at which air is displaced in the process of supplying the inert gas to the space between the casting rolls 120 and the meniscus shield 140 through the focused gas supply nozzle 150.

In an example, the air discharging unit 160 may include an air discharging pipe 162 disposed on one side of the meniscus shield 140, and a valve 164 adjusting the opening and closing of the air discharging pipe 162.

The air discharging unit 160 may discharge the air displaced by the inert gas supplied through the focused gas supply nozzle 150.

FIG. 4 is a graph illustrating the relationship between a supplied amount of nitrogen and an oxygen removal time obtained from a twin-roll strip caster according to an exemplary embodiment.

Referring to FIG. 4, the focused gas supply nozzle 150 may have, for example, a cross section of 16.6 cm², and may supply inert gas, for example, nitrogen, through the cross section. It can be seen that when the nitrogen is supplied at a flow rate of 2,500 liter/min and the concentration of oxygen is less than or equal to 100 ppm, if the air discharging unit 160 is opened to supply the nitrogen, the flow rate may be increased by about 70% as compared to a state in which the air discharging unit 160 is closed.

As set forth above, according to an exemplary embodiment, a twin-roll strip caster, which may supply inert gas to a space between casting rolls and a meniscus shield in an early stage of a casting process before molten steel is supplied to the space to create an inert atmosphere in a space between the casting rolls, so that the molten steel may not contact air, thus preventing scum from being generated.

While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims. 

What is claimed is:
 1. A twin-roll strip caster comprising: a pair of casting rolls rotating in opposite directions to each other, and having an edge dam adhering to both end surfaces of the casting rolls in a length direction of the casting rolls; a submerged nozzle discharging molten steel between the pair of casting rolls; a meniscus shield disposed above the molten steel supplied through the submerged nozzle to prevent the molten steel from contacting air; and a focused gas supply nozzle disposed between the submerged nozzle and the meniscus shield to supply inert gas therebetween so as to displace air between the submerged nozzle and the meniscus shield before the molten steel is supplied.
 2. The twin-roll strip caster of claim 1, wherein the focused gas supply nozzle is disposed in the meniscus shield to dispense the inert gas to surfaces of the pair of casting rolls between the submerged nozzle and the edge dam.
 3. The twin-roll strip caster of claim 1, wherein the focused gas supply nozzle dispenses the inert gas from above one casting roll to a surface of the other casting roll.
 4. The twin-roll strip caster of claim 3, wherein the focused gas supply nozzle comprises: a first focused gas supply nozzle dispensing the inert gas from above the one casting roll, positioned at one end of the submerged nozzle in a width direction, to the surface of the other casting roll; and a second focused gas supply nozzle dispensing the inert gas from above the other casting roll, positioned at the other end of the submerged nozzle in the width direction, to the surface of the one casting roll.
 5. The twin-roll strip caster of claim 1, further comprising an air discharging unit disposed on one side of the meniscus shield to discharge air.
 6. A casting method for a twin-roll strip caster comprising: an assembling operation of combining a pair of casting rolls, a preheated edge dam, a preheated submerged nozzle, and a meniscus shield with one another; an inert gas supplying operation of displacing air remaining between the pair of casting rolls and the meniscus shield by supplying inert gas therebetween at high pressure before molten steel is supplied through the preheated submerged nozzle after the assembling operation; and a casting operation of supplying the molten steel through the submerged nozzle after air is displaced by the inert gas supplying operation.
 7. The casting method of claim 6, wherein the inert gas supplying operation comprises supplying the inert gas between the preheated edge dam and the preheated submerged nozzle.
 8. The casting method of claim 6, wherein the inert gas supplying operation further comprises an air discharging operation of discharging air remaining between the pair of casting rolls and the meniscus shield while the inert gas is supplied.
 9. The casting method of claim 6, wherein the inert gas supplied in the inert gas supplying operation is supplied at a flow rate of 500 liter/min to 2,500 liter/min. 